The high prevalence of trauma in the US and around the world has made epidemiologic research on the sequelae of stressful and traumatic experiences of paramount importance. Unfortunately, large longitudinal cohorts of people who have experienced traumatic events, or received a psychiatric diagnosis as a result of these events, do not exist in the United States and cannot be easily constructed. General population cohorts that do exist are often limited in the amount of data that can be collected due to considerations about survey length, and are vulnerable to bias and loss to follow up. Denmark is the ideal location in which to study the longitudinal sequelae of disorders resulting from traumatic experiences, as national healthcare and social records have been catalogued for decades. The current application aims to create an ICD-10 reaction to severe stress (RSS) cohort in Denmark (including people with the diagnoses of acute stress reaction, posttraumatic stress disorder, adjustment disorder, and other reactions to severe stress), which can then be linked to other national Danish healthcare and social data to study various long term effects of these disorders. National Danish databases will also be used to collect data about traumatic events that have been experienced by all members of the cohort, where possible. Given that the current study proposes to use existing national healthcare data, the RSS cohort will ultimately provide an efficient resource to examine the short and long-term sequelae of RSS disorders, as well as modifiers of these associations. [Therefore, this project is well-suited to further the current NIMH strategic objective of charting mental illness trajectories to determine when, where and how to intervene (#2).] Further, the proposed open cohort will be an enduring resource, which can be continually updated to examine associations. Finally, because the cohort will contain prospectively collected data on all people who have ever received an ICD-10 RSS diagnosis in Denmark, the research produced from the proposed cohort will not be subject to the recall and selection bias issues common in studies that rely on retrospective reporting within subsets of populations. As an initial demonstration of the utility of the new cohort, we wil examine the associations between ICD-10 RSS disorders and all-cause mortality and mortality due to suicide.